The membrane thingy is junk.
Might be okay for a tiny tank, but it's no better than a bell type diffusion method, you can increase the ability of it to add CO2 by placing more current need it, across the gas layer etc just like any passive bell diffuser, it's passive, thus has very low capcity to diffuse much CO2 into the water, so what if it's 100% when you need far more than it can dissolve into the water!!
Takes a lot more and passive diffusers are not very good for anyone really.
You do much better with a disc or a rector with a powerhead/flow from a filter etc.
The redsea thingy is a take off on my old reactor desgn some 10 years ago which modified the gravel vac idea.
For the cost of a Rio 180 powerhead and 2-3$, you can easily make a DIY CO2 reactor that will outperform everything you have listed here.
See this thread:
http://www.aquariacentral.com/forums/showthread.php?t=75010&highlight=DIY+CO2+reactor+Tom+Barr
and this one:
http://www.aquariacentral.com/forums/showthread.php?t=75015
http://www.aquariacentral.com/forums/showthread.php?t=82321
Not sure why folks would pay 30-50$ a shipping for something that literally takes all of 15 min tops to make it + it works much better.
Veiwtainers can be bough at Home Depot OSH etc for 1.99 for the 4"Lx 2" dia tube or on line at Viewtainer.com
Very simple to make a very effective,
You can monkey around with CO2 and complain about algae a long time before figuring out that it pays to do the CO2 right.
I've seen folks frustrate themselves for years.
A glass disc and blasting the mist from that all around the tank in a good pattern will also work very well.
Regards,
Tom Barr